CIE Nov 2014 v5 Paper 3 Q2

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PMT In this experiment you will determine the enthalpy change, H, for the dehydration of hydrated sodium carbonate to anhydrous sodium carbonate. Na2CO3.xH2O(s)Na2CO3(s) + xH2O(l) In order to do this,rst you will determine the enthalpy changes for the reactions of anhydrous sodium carbonate and hydrated sodium carbonate with excess hydrochloric acid. Then you will use Hess Law to calculate the enthalpy change for the reaction above. FA 4 is anhydrous sodium carbonate, Na2CO3. FA 5 is hydrated sodium carbonate, Na2CO3.xH2O. FA 6 is 4.0 mol dm3 hydrochloric acid, HCl. (a) Determination of the enthalpy change for the reaction of anhydrous sodium carbonate, FA 4, with excess hydrochloric acid. MethodSupport a plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. Record the initial temperature of the acid. Weigh the container with FA 4 and record the mass. Slowly add all the FA 4 to the acid in the plastic cup. Note that the reaction will be vigorous. Avoid inhaling any acid spray produced. Stir constantly until the maximum temperature is reached. Record the maximum temperature. Weigh the container from which you added FA 4 and record the mass. Calculate and record the mass of FA 4 used and the temperature rise.UCLES 2014 9701/35/O/N/14 [3] [Turn over<br /> (b) Calculation (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] PMT (ii) Calculate the number of moles of anhydrous sodium carbonate used. [Ar: C, 12.0; O, 16.0; Na, 23.0] energy produced =J (iii) Calculate the enthalpy change, in kJ mol1, for the reaction below. Na2CO3(s) + 2HCl (aq)2NaCl (aq) + CO2(g) + H2O(l) moles of Na2CO3 =mol enthalpy change for anhydrous Na2CO3 =kJ mol1 sign value [3]UCLES 2014 9701/35/O/N/14<br /> PMT (c) Determination of the enthalpy change for the reaction of hydrated sodium carbonate, FA 5, with excess hydrochloric acid. MethodSupport the second plastic cup in the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. Record the initial temperature of the acid. Weigh the container with FA 5 and record the mass. Slowly add all the FA 5 to the acid in the plastic cup. Note that the reaction will be vigorous. Avoid inhaling any acid spray produced. Stir constantly until the minimum temperature is reached. Record the minimum temperature. Weigh the container from which you added FA 5 and record the mass. Calculate and record the mass of FA 5 used and the temperature decrease. (d) Calculation (i) Calculate the energy absorbed during this reaction. [Assume that 4.2 J are absorbed when the temperature of 1.0 cm3 of solution falls by 1.0 C.] [2] energy absorbed =J (ii) Use your answer to 1(c)(vi) to calculate the number of moles of hydrated sodium carbonate, Na2CO3.xH2O, used. [Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0] (If you were unable to calculate x in 1(c)(vi), you may assume that x = 8. Note: this is not the correct value.)UCLES 2014 9701/35/O/N/14 [Turn over moles of Na2CO3.xH2O =mol<br /> (iii) Calculate the enthalpy change, in kJ mol1, for the reaction below. Na2CO3.xH2O(s) + 2HCl (aq)2NaCl (aq) + CO2(g) + (x + 1)H2O(l) PMT enthalpy change for Na2CO3.xH2O =kJ mol1 sign value [2] (e) Use your values for the enthalpy changes calculated in (b)(iii) and (d)(iii) to calculate the enthalpy change for the reaction below. Na2CO3.xH2O(s)Na2CO3(s) + xH2O(l) Show clearly how you obtained your answer. (If you were unable to calculate the enthalpy changes, you should assume that the value in (b)(iii) is43.1 kJ mol1 and the value in (d)(iii) is +32.8 kJ mol1. Note: these are not the correct values.) enthalpy change =kJ mol1 sign value [2] (f) A student suggested that the experiments carried out in (a) and (c) would be more accurate if double the volume of hydrochloric acid had been used, but with hydrochloric acid of concentration 2.0 mol dm3, instead of 4.0 mol dm3. State and explain whether or not you agree with the students suggestion.[1] [Total: 13]UCLES 2014 9701/35/O/N/14<br />

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